Hi, guys. I'm sure someone out there can help.
I've been an electronics engineer all my working life, but on industrial control circuitry, never organs.

Now I have reached that certain age, when time is no problem, I have bought an old B200. Everything works, except a 16' drawbar that only sounds when pulled out beyond 4.
Hooked up to a 860 cabinet, it sounds fabulous, except that when it has been running for an hour or so, one key (C3) sounds softly, through whichever drawbar(s) is(are) pulled.

Can someone point me to a beginner's book (?) on the fundamental hierarchy of electronic organs. For instance, is there one oscillator divided down, or one for each pitch?
What is the basic method for enabling a frequency to travel through to the amplifier, ie how does a note sound when it's key is pressed?

The experts among you may well think "Supposedly an electronics engineer - why doesn't he read the circuit diagrams". I have, and they make sense (to me) electronically, but I cannot get my head round the basic philosophy!

Please help.

Thanks in advance, Pete